1. Field of the Invention
The present invention generally relates to a performance analysis tool that may be used to automatically generate reliability curves as well as other performance analysis charts based on data obtained from a set of desired data records which may be randomly dispersed within a larger unsorted record set. The present invention also provides a method for automatically generating reliability curves as well as other performance analysis charts based on bit run records data.
2. Background Art
Oil and gas are typically obtained from subterranean earth formations by drilling bore holes from the surface to the subterranean earth formations. FIG. 1 shows one example of a conventional drilling system used to drill bore holes through earth formations. The drilling system includes a drilling rig 10 used to turn a drill string 12 that extends downward into a bore hole 14. Connected to the end of the drill string 12 is a drill bit 20. Drill bits used for drilling bore holes through earth formations typically include roller cone drill bits and fixed cutter drill bits. The drill bit shown in FIG. 1 is a roller cone drill bit. A more detailed example of a roller cone drill bit is shown in FIG. 2.
Referring to FIG. 2, the drill bit 20 includes a bit body 22 having an externally threaded connection at one end 24, and a plurality of roller cones 26 attached to the other end and able to rotate with respect to the bit body 22. Attached to the cones 26 are a plurality of cutting elements 28 typically arranged in rows about the surface of the cones 26. The cutting elements 28 may be inserts, such as tungsten carbide inserts or polycrystalline diamond compacts, or milled steel teeth. Hardfacing (not shown) may also be applied to the cutting elements 28 and other portions of the bit 20 to reduce wear on the bit 20 and to increase the life of the bit 20 as the bit 20 cuts through earth formations.
As shown in FIG. 2A, each roller cone 26 is mounted on a steel journal or pin 32 typically formed integral with the bit body 22. The roller cone 26 is held on the journal 32 by journal bearings 30 which allow the roller cone 26 to rotate with respect to the journal 32 when cutting elements 28 on the roller cone 26 contact earth formation at the bottom of the bore hole (16 in FIG. 1) during drilling.
One example of a fixed cutter drill bit is shown in FIG. 3. The fixed cutter drill bit 40 includes a bit body 42 having an externally threaded connection at one end 44, and a plurality of blades 46 extending from the other end of bit body 42 and forming the cutting surface of the bit 40. A plurality of cutters 48 are attached to each of the blades 46 and extend from the blades to cut through earth formations when the bit 40 is rotated during drilling. The cutters 48 deform the earth formation by scraping and shearing. The cutters 48 may be tungsten carbide inserts, polycrystalline diamond compacts, or any other cutting elements formed of materials hard and strong enough to cut through the formation.
When components of a drill bit wear out or fail as a bore hole is being drilled, the bit must be withdrawn from the bore hole and replaced with another bit. The time required to replace a bit is significant and is essential time lost during drilling operations. This time can become a significant portion of the total drilling time, and thus very costly, particularly as the bore hole depths become great. Therefore drill bits having reliably long service life are desired for drilling operations to maximize the effectiveness of the time spent drilling.
The need to replace a bit during a drilling operation is often indicated at the surface by a significant drop in the rate of penetration achieved by the bit. Replacement of a drill bit may be required for a number of reasons, such as severe wear or failure of one or more journal bearings (30 in FIG. 3) or seals. The bearings can be friction or roller-type bearings, which can be subject to high loads, high hydrostatic pressures in the hole being drilled, high temperatures due to drilling, as well as harmful abrasive particles originating from the formation being drilled. Bits may also be replaced because of excessive wear, breakage, or loss of cutting elements contacting and breaking up the formation, or the loss or failure of other components of the bit.
Drilling operators take great care in attempting to always pull bits and replace them just before or soon after a bearing failure or other failure of the bit occurs to avoid the risk of losing large portions of a bit in the bore hole. When portions of bits fail and break off in the bore hole, these portions must typically be retrieved before drilling can be resumed. Retrieving portions of a bit that have broken off in a bore hole is typically difficult, expensive, and time consuming. Therefore, being able to predict the performance or risk of failure of a bit used for drilling is desired so that bits can be pulled from a bore hole before catastrophic failure occurs.
To predict when a bit should be pulled from a well bore, drilling operators generally look at past performances of similar bits. To facilitate this analysis, drilling operators typically record all aspects associated with a drilling operation. When the bit being used for drilling is pulled to the surface, the condition of the bit is also carefully examined and other parameters characterizing the final condition of the bit are recorded, such as grades indicating the worn or failed condition of the cutting elements bearings/seals, etc., as well as the final depth and footage drilled by the bit. In this way, data characterizing each segment of drilling is obtained to capture a complete characterization of the drilling operation.
Data recorded for each drill bit used during a drilling operation may be stored in a database (“bit records database”). Each record in a bit records database typically corresponds to the use of a single drill bit used during a particular drilling operation. Bit records may be collected for drilling operations that occur all over the world at various times. Data from the records stored in a database can later be used for performance analysis studies, such as to analyze the performance of a particular style or group of bits, to develop performance verification techniques for bits, to perform comparisons of different bit products by different manufactures, and/or to calculate reliability curves which can be used to predict when a bit may need to be pulled during a drilling operation to avoid catastrophic failure. The data from these records may also be particularly useful to bit manufactures to identify areas of improvement needed in their bit designs to improve product performance and illuminate the longevity of components of their bits, such as the cutting elements, bearings and seals compared to their competitors.
To perform bit performance analysis studies, data is typically reviewed by an engineer or skilled practioner who filters data from the bit runs and uses the filtered data to generate graphical representations summarizing the performance of various bits. These graphical representations typically include graphs, tables or charts showing performance parameters for different groups of bits. The data may also be used by skilled practitioners to calculate reliability curves for selected groups or types of bits.
Data from the bit records can be used to calculate the reliability of a family or group of bit based on the recorded condition of the bits, such as whether seals or bearings failed during drilling. To determine the reliability of a family of bits, the following reliability equation may be used is:
                                          R            ^                    ⁡                      (                          t              i                        )                          =                                            N              +              1              -              i                                      N              +              2              -              i                                ⁢                                    R              ^                        ⁡                          (                              t                                  i                  -                  1                                            )                                                          (                  Eq          .                                          ⁢          1                )            wherein N is the total number of bits being considered, i is the rank of a current bit that failed, ti is the time corresponding to the current failure, ti-1 is the time corresponding to the previous failure, and {circumflex over (R)}(·) is the reliability of the functioning feature at the indicated time. Various equations for calculating a reliability or confidence level for a function of a member are known in the art. See for example, Lewis, E. E., Introduction to Reliability Engineering, N.Y., John Wiley & Sons, 1987. p. 121-211.
Reliability equations are commonly used to evaluate life-related performances, such as failure of components, such as bearings or light bulbs or the life expectancy of patients on various medications. These types of equations also may be used to predict the life and performance of bits used to drill bore holes in earth formations, such as to predict bearing/seal life. In the prior art, reliability curves for predicting effective bit life and bit performance were calculated one data point at a time with a hand calculator after spending a significant amount of time identifying and manipulating the data used to calculate the reliability curve.
Conventional methods used first required manually going through and examining data records to identify records containing “good” data for calculating the reliability. Records corresponding to a desired group or family of bits are then selected for use in calculations. Once the desired records are selected, data in the records corresponding to a time parameter (parameter to represent time) is selected from the records. Examples of time parameters include hours drilled, feet drilled, revolutions or total energy for a bit during drilling. Then the corresponding data in the records indicating the condition of the component for which the reliability is to be calculated is selected. Examples of functional conditions recorded for components in bit records include conditions such as failure of the bearing/seal or the wear condition of the cutting structure. For features that are graded using codes or numbers, the function condition may be considered failed if the grade is beyond a certain value, and the data for the function condition may be replaced by a Boolean indicator, such as a 0 or 1 to indicate whether the function will be considered effective or failed, respectively, for the given analysis. Once the time parameter data and the corresponding component condition data are collected, the data is ranked (reordered) in ascending order based on the value of the time parameter for each record. Then the data is indexed in ascending order to indicate the ranking of each record. After that, a hand calculator or computer programmed with the reliability function may be used to calculate, one by one, the reliability associated with each of the records having a failed function based on the time related index given to the record. Once the reliability values are calculated, they can then be plotted with respect to the corresponding time parameter values to generate the reliability curve for the selected feature of the selected group of bits.
Using the conventional method for calculating reliability described above, when the reliability based on a different time parameter or for an altered group of data is desired, the previously ordered and ranked data has to be discarded because data sorted and ranked based on the old time parameter is no longer useful. Then the group of desired records must be reselected (if the group is altered), new data corresponding to the newly selected time parameter and component parameter is selected from the group of records, reconditioned (to include Boolean function indications), and resorted based on the value of the newly selected time parameter. Then the data is re-ranked, and the reliability calculated for the functions indicated as failed in the data.
Calculating reliability values using the above conventional method can be laborious, especially when 20 or more bit records are considered, or when the reliability of several different groups of bits is desired for a comparison. Therefore, bit performance based on the reliability of bit life, while extremely useful, has not been widely practiced. Currently, reliability charts that are generated involve a very limited number of bit runs because of a lack of capability for the easy creation of reliability curves. Furthermore, most bit companies do not use reliability curves or other statistical data in an analysis of their bits because of the difficulty, skill level and experience involved in correctly calculating and generating these curves. Also because reliability curves in the past have been generated manually by various individuals, errors may frequently occur and no standard format or layout has been set for producing these types of curves or other performance charts desired from a performance analysis.
Other charts desired in a performance analysis study are also typically generated manually. This is typically done by first obtaining data records from a database. Then, depending on the type of chart desired, locating the data field containing the desired data and selecting the desired data from the records. Calculating performance analysis values as needed and then arranging and formatting the data as needed for input into a graphics generator to generate the performance chart desired. Titles, legends and other aspects of the charts must then be defined. This procedure is repeated to produce each performance chart desired, one at a time. As a result, the production of a complete set of performance charts can take hours or days.
To reduce the time and skill level required to generate quality reliability curves, and other performance charts, a tool providing the ability to more easily calculate values for generating these performance charts is greatly desired by both drilling operators, in selecting bits, and drill bit manufactures in identifying performance issues with their bits.